The invention relates broadly to a packer tool for plugging off a well casing. More specifically, the invention covers a packer tool of the permanent type.
In the production of oil and gas there are various downhole operations which require plugging off the well casing at a given point, or at more than one point. Examples of such operations are hydraulic fracturing of a producing zone, and placing of propping materials, such as sand, in the fracture opening. When such operations are to be performed, the well casing is usually plugged off with a packer tool, either a permanent-type packer, or a retrievable packer.
The packet tools now available are not entirely satisfactory because of various problems. A major problem is in the "setting" of the packer in the casing. When force is applied from the wellhead, to "set" the tool in place, the teeth of the upper and lower slips on the tool grip into the casing wall simultaneously. At the same time, the rubber packing elements are only partly compressed, so that they do not set tightly against the casing wall. As additional force is applied, to further set the packing elements, the packer tool moves down and the slips drag along the casing wall. This causes the slip teeth to become dull in a very short time, and the packer is then unable to form a good fluid-tight plug in the casing.
The packer tool of this invention, which is designed to be permanently set in a well casing, avoids the problem described above. This tool is designed such that the lower slips are set first, followed by setting of the upper slips, with only a slight movement of the packer in the casing during the setting operation.
The tools described in U.S. Pat. Nos. 2,753,941 (Hebard et al.), 3,061,013 (Williams), and 3,517,742 (Thomas) are representative of prior art packers and bridging plugs which are used in plugging off a well casing to perform a downhole operation. Although the tools described in these references are suitable for plugging off a well casing, the structure and operation of each tool is substantially different than the packer tool of the present invention. In particular, none of the prior tools have the capability for setting the slip members in the manner of the present packer, to avoid the drag problem described above.